A railroad frog is a device which is inserted at the intersection of a mainline rail and a turnout line rail to permit the flanges of wheels moving along one of the rails to pass across the other. The frog supports the wheels over the missing tread surface between the frog throat and the frog point and provides flangeways for aligning the wheels when passing over the point so that they will be afforded the maximum load bearing area. Generally, standard turnout frogs may be classified as rigid frogs which have no movable parts or movable wing frogs in which one or both of the wings move outward to provide flangeways for railroad car wheels. Rigid frogs include manganese railbound frogs, solid manganese frogs and self guarded frogs. Movable frogs include railbound manganese spring frogs.
Rigid railbound manganese frogs are constructed by combining carbon steel rails with manganese steel castings. These frogs are preferred over frogs which do not encompass manganese castings inasmuch as manganese steel has a resistance to abrasion and impact which exceeds that of carbon steel by as much as ten times.
In a conventional American Railroad Engineering Association (A.R.E.A.) standard railbound frog installation, a frog casting which may be manganese is clamped between a pair of wing rails. Laterally extending fit pads are formed on opposite sides of the frog casting to assist in positioning the casting with respect to the wing rails which support the casting. The fit pads are machined to complement the contour of the wing rail head and base fishing surfaces and the rail web which extends therebetween. Commonly, laterally extending bolts project through bores in the wing rails and the frog casting to secure the wing rails to the casting. This serves to locate the wing rails and the frog casting such that the required gauge lines are maintained. The bolted assembly further helps prevent longitudinal movement of the rails due to thermal expansion and contraction.
Manganese steel has a resistance to abrasion and impact which greatly exceeds that of carbon steel. In part, this is because of the metal's inherent ability to work harden. Although manganese steel's extreme resistance to abrasion makes it preferred for heavy rail traffic usage such as in frog areas, this same characteristic makes the metal extremely difficult to machine. The material does not conform to traditional guidelines for machining steel. Instead, manganese steel requires very low rates of feed and slow cutter speeds. Machine tool cutters must be configured to allow for very heavy cuts with high chip loads inasmuch as all material must be removed from each surface in a single tool pass due to the work hardening characteristics of the metal. Cutter tool life is short even where the inserts are formed from special grades of carbide and ceramic materials. The conventional A.R.E.A. railbound manganese frog casting requires extensive machining of relatively complex shapes. The fit pads must be shaped to complement the webs and fishing surfaces of wing rails as stated above. Additionally, in a traditional frog the frog casting rests upon the angled fishing surface of the wing rail bases along the entire length of the interface between the casting and the wing rails this being the full length of the casting. This is illustrated in FIG. 3 of the drawings. Consequently, the entire bottom surface of the casting must be machined on both sides. This is time consuming and expensive.
Because the frog casting rests upon the fishing surfaces of the wing rail bases, loads borne by the tread surface of the casting are transmitted downwardly through the vertical side walls of the casting directly into the angular rail bases. This results in a grating action between the casting and the rail base mating surfaces due to the cyclic loading imposed therein by each passing rail car wheel. The grating action causes the surfaces to abrade which ultimately loosens the fit between the surfaces. Additionally, a portion of the vertical loads imposed upon the tread surface and side walls of the casting result in a lateral component of force being imposed upon the wing rail bases. This of course results because the load is not imposed at right angles to the base. The lateral force tends to bias the wing rails laterally outwardly from the casting. This loading tends to loosen the interface between the ring rails and the casting and imparts a tensile load to the bolts which clamp the casting between the wing rails. The cyclical tensile loading can result in failure of bolt assemblies and ultimate failure of the frog assembly.
Despite the inherent strength of manganese steel, higher train speeds and greater wheel loading which have become more prevalent in recent times have caused manganese frogs to exhibit evidence of failure after prolonged usage. Such failure has included crushed or collapsed tread areas believed to be symptomatic of shrinkage voids in the casting and spreading of the gauge lines both due to heavy wheel loads.
One type of frog casting which addressed these problems resulted in a railbound manganese frog having a "boxed-in" design commonly referred to as an "integral base" configuration. This structure has a bottom surface which sometimes is co-planar with the base surface of the wing rails and also has a continuous interface between the lower portion of the casting side wall and the upper angled or fishing surface of a wing rail flange. This interface extends the entire length of a casting. This design structure utilizes a longitudinally extending center wall or rib which extends between the underside of the upper running surface and the horizontal bottom wall. A significant degree of success was achieved with this design in terms of preventing crushing of the casting tread areas.
However, difficulties were encountered in the manufacture of the frog casting. It was found that the extensive use of sand cores in the drag portion of the mold which cores were required to produce the internal cavities resulted in chronic porosity of the casting. This porosity resulted from gases emanating from the breakdown of the organic binding agents utilized to harden the sand cores. Additionally, because of the large number of cores used in making the casting, problems frequently were encountered with non uniform cross-sectional thicknesses due to shifting of the cores in the drag portion of the mold.
While an integral base casting having a central longitudinally extending rib has substantially increased the life over that of a conventional manganese frog casting, it was desirable to develop a railbound manganese frog which would achieve greater casting life while reducing the complexity of the casting both in terms of internal passages and in terms of the amount of machining required to enable the casting to be fit to the wing rails.
The instant invention achieves this objective with a direct support railbound manganese frog having a frog casting which is clamped between mainline and turnout line wing rails but is freestanding such that substantially the entire bottom surface of the casting is spaced from the base of the wing rails and rests directly upon rail plates or other rail support structure. Consequently, the loads imposed on the casting by rail car wheels passing over the tread surfaces thereof are transferred directly into the frog supporting structure such as rail plates thus bypassing the wing rails themselves. This is accomplished by positioning the vertical side walls of the frog casting immediately below the load bearing surfaces and extending the walls downwardly to the base plate. To accomplish this, the inner base flange of each wing rail is cut away to provide clearance for the adjacent casting side wall. With this direct support frog design, abrasion between the frog casting and the wing rails is eliminated and no lateral loads are transmitted through the rail to the bolts which clamp the wing rails and frog casting together to form a railbound manganese bound assembly.